In this study, we propose an electrochemical immunoassay into a disposable microfluidic platform, using quantum dots (QDs) as labels and their enhanced detection using bismuth as an alternative to mercury electrodes. CdSe@ZnS QDs were used as label to detect human IgG as a model protein and detected through highly sensitive stripping voltammetry of the dissolved metallic component (cadmium in our case). The modification of the screen printed carbon electrodes (SPCEs) was done by a simple electrodeposition of bismuth which was previously mixed with the sample containing QDs. A magneto-immunosandwich assay was performed using a micromixer and a magnet placed at its outlet in order to capture the magnetic beads (MBs) used as solid support for the immunoassay. SPCEs were integrated at the end of the channel as detector. Different parameters such as bismuth concentration, flow rate, and incubation times, were optimized. The limit of detection for HIgG in presence of bismuth was 3.5 ng mL−1 with a relative standard deviation (RSD) of 13.2%. This LOD was about 3.3 fold lower than the one obtained without bismuth. Furthermore, the sensitivity of the system was increased 100 fold respect to experiments carried out with classical SPEs, both in presence of bismuth.